在低吸積率時黑洞相對論性噴流的形成

觀測上黑洞吸積系統(accreting black hole systems)的光度(Luminosity),L,與電波輻射(radio emission)的互相關聯暗示了黑洞吸積盤(accretion disk)與噴流有偶合關係。假設黑洞相對論性噴流(relativistic jets)是藉由旋轉黑洞的轉動動能提供能量，我們檢視了當黑洞吸積盤隨其光度(以愛丁頓光度(Eddington Liminosity)，LEdd，為單位)變化而改變種類時，黑洞的能量是否能被抽取出來(產生噴流)。在此論文中，我們主要討論相對論性噴流為何能夠在吸積盤成為薄盤狀前產生(當L/LEdd 漸漸接近約0.01前)。經由相對論性流體力學(general relativistic magnetohydrodynamics)的討論，我們發現黑洞轉動能量容易在黑洞被一種混合外部薄盤(thin disk)及內部水平對流主導吸積流(advection-dominated accretion flow)的吸積盤所包圍時,經由"磁流體Penrose過程(MHD Penrose Process)"被抽取出來。這類混合薄盤與水平對流主導吸積流的吸積盤曾經被用來解釋黑洞X射線雙星(black hole X-ray binaries)和活躍星系核(active galactic nuclei)的光譜表現。我們的模型也解釋了為何射電光度與噴流速度兩者皆隨著X射線光度上升而增加。此外，我們提出關於為何當L/LEdd約等於0.01時噴流被抑制，以及為何在L/LEdd 大於 0.01和 L/LEdd 小於0.01時產生的噴流有不同的功率(power)和速度的可能解釋。我們建議，對於不同種類的吸積盤，在黑洞視像地平面(event horizon)附近，當吸積流速度從次音速到超音速時的吸積流幾何形狀(transonic flow geometry)，以及被吸積盤束縛的大尺度磁場兩者對抽取黑洞轉動動能及噴流的產生有重要的影響。

關鍵字

黑洞物理；吸積盤；磁流體力學； X射線雙星；活躍星系核；磁場

並列摘要

Observed correlations between the disk luminosity (L) and radio emission from accreting black hole (BH) systems indicate underlying couplings between BH accretion disk and jet. Assuming relativistic jets are launched at the expense of the rotational energy of spinning BHs, we examine whether the BH energy can be extracted outward when the accretion disk type varies with L/LEdd, where LEdd is the Eddingtion luminosity. In this thesis, we mainly focus on why relativistic jet is launched before the disk is dominated by the thin disk type (before L/LEdd approaches the value ∼ 0.01), as inferred from observation. Considering the general relativistic magnetohydrodynamics (MHD), we found the extraction of BH energy via the “MHD Penrose process” (and hence the relativistic jet)can preferentially take place when the BH is surrounded by a disk which consists a (outer) thin disk and an (inner) advection-dominated flow. Such combined disk has been inferred from the spectra of both BH X-ray binaries and active galactic nuclei. Our model also consistently explains why both the radio luminosity and jet speed increase with increasing X-ray luminosity. In addition, we propose possible explanations why jet are quenched at when L/LEdd ∼ 0.01 and why the jets launched when L/LEdd > 0.01 has different jet power and jet speed than those launched when L/LEdd < 0.01. It is suggested that, for different types of accretion disks, both the transonic flow geometry near the horizon, and the large–scale magnetic field confined by the disk, play essential roles in affecting the extraction of BH rotational energy and hence the jet formation.

並列關鍵字

black hole physics ； accretion disk ； magnetohydrodynamics ； X-ray binaries ； active galactic nuclei ； magnetic field

參考文獻

Komissarov, S. S. 2005, Monthly Notices of the Royal Astronomical Society, 359, 801

Manmoto, T., Kato, S., Nakamura, K. E., & Narayan, R. 2000, Astrophysical Journal, 529, 127

Narayan, R., Kato, S., & Honma, F. 1997, Astrophysical Journal, 476, 49

Abramowicz, M. A., Chen, X., Kato, S., Lasota, J.-P., & Regev, O. 1995, Astrophysical Journal Letters, 438, L37

Igumenshchev, I. V., Chen, X., & Abramowicz, M. A. 1996, Monthly Notices of the Royal Astronomical Society, 278, 236

國際替代計量

在低吸積率時黑洞相對論性噴流的形成

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